Siemens SINUMERIK 840Di Function Manual page 1793

The basic orientation is always the direction perpendicular to the plane in which tool radius
compensation is performed. With turning tools, in particular, the tool orientation generally
coincides with the longitudinal tool axis.
The setting data specified below are effective only if the basic orientation of the tool is
defined by an entry in at least one of the system variables $TC_DPVx[t, d].
They have no effect if the tool orientation is only determined by the plane selection G17 -
G19 and is compatible with previous behavior.
If setting data:
SD42950 $SC_TOOL_LENGTH_TYPE
is not equal to zero, the plane of the basic orientation for a cutting edge is treated either like
a milling tool or like a turning tool, irrespective of the entry in $TC_DP1.
Plane change
A change of plane causes a change in orientation.
The following rotations are initiated:
When changing from:
G17 ⇒ G18:
G18 ⇒ G19:
G19 ⇒ G17:
G17 ⇒ G19:
G18 ⇒ G17:
G19 ⇒ G18:
These rotations are the same as those that have to be performed in order to interchange the
components of the tool length vector on a change of plane.
The basic orientation is also rotated when an adapter transformation is active.
If setting data:
SD42940 $SC_TOOL_LENGTH_CONST
is not equal to zero, the tool orientation is not rotated on a change of plane.
Tool length components
In relation to setting data:
SD42910 $SC_MIRROR_TOOL_LENGTH
and
SD42950 $SC_TOOL_LENGTH_TYPE,
tool orientation components are treated in the same way as tool length components, i.e., the
components are interchanged accordingly and assigned to the geometry axes.
Tool Compensation (W1)
Function Manual, 08/2005 Edition, 6FC5397-0BP10-0BA0
2.7 Basic tool orientation
Rotations
Rotation through -90 degrees about the Z axis
followed by rotation through -90 degrees about
the X axis
Rotation through 90 degrees about the X axis
followed by rotation through 90 degrees about the
Z axis
Detailed Description
2-113